In the manufacture of some types of rigid pin-populated printed wiring boards, as many as 10,000 terminal pins are inserted into apertures of each of the boards. The boards are referred to as backplanes and typically measure eight inches by twenty-two inches on their sides. The pins electrically engage portions of printed wiring on the backplanes to provide for connections to external circuits. Typically, the spacing between adjacent apertures on each backplane is extremely small. For example, the spacing between apertures on one backplane is 0.125 inch. Further, each terminal pin typically has a square cross section of, for example, 0.025 inch except in those areas where the pin is formed with (1) lateral ears having a push shoulder and (2) an aperture-engaging portion intermediate the ends thereof. The pin is relatively slender and typically measures one and one-half inches in length.
Each of the pins have slender shank portions which extend from opposite sides of the backplane. After the pins have been assembled with the backplane, the backplane is mounted in a frame where external wiring is wire wrapped to the pins on one side of the backplane commonly referred to as the wiring side. Other printed wiring boards, referred to as circuit packs, have electronic components electrically and mechanically secured thereto and have connectors secured to one end thereof. The connectors of these boards ultimately are inserted over selected ones of the pins extending from the other side of the backplane commonly referred to as the component side.
During the insertion of the pins into the apertures of the backplane and during subsequent handling of the pin-populated backplane, some of the pins may be bent undesirably. For example, the most severely bent pins may deviate from an axial centerline by 0.050 inch in any direction. Consequently, adjacent pins which are bent in opposite directions could have a deviation swing of 0.100 inch.
Since the component side of the pins are destined for insertion into a connector, and the pins on the wiring side may be wired by an automatic wiring facility, it is important that the pins be axially straight and perpendicular to the plane of the backplane within an acceptable tolerance. Otherwise, a slightly bent pin on the component side, for example, could be misaligned with its mating aperture in the connector. As the connector is moved into place, the bent pin would engage the face of the connector and would be bent further towards the surface of the backplane thereby failing to provide the required electrical connection.
Since the pins are located on a grid spacing of 0.125 inch, and since the pins have a square cross section of 0.025 inch, the facing portions of adjacent pins are 0.100 inch apart. Consequently, it is most difficult to provide a facility for straightening pins which are so closely arranged. For example, a straightening facility typically is positioned over the tip of the pin to be straightened and is then moved in a selected motion whereby the walls of the opening engage and move the pin close to the centerline of the opening. To accomplish this straightening operation, a pin-receiving opening of the facility must be slightly larger in cross section than the cross section of the pin. Further, to insure that a bent pin will enter the pin-receiving opening, the mouth of the opening should be formed with a tapered or conical lead-in portion of sufficient dimension to receive any pin having a deviation as severe as 0.050 inch. Thus, the conical lead-in portion of the opening would require additional space in the cross section direction. In addition, the facility must have some bulk around the pin-receiving opening to provide for the opening and the conical lead-in portion. Thus, it is apparent that, with the close spacing between adjacent pins, it is most difficult to provide a sturdy facility which can accomplish the straightening of the pin.
Still another problem encountered in straightening the pins is due to warpage of the backplane after the pins have been inserted into the backplane. Such warpage is due to the pin density and the interfacial relationship between the apertures and the pins. Consequently, while any pin may be perpendicular with the backplane, if the backplane is warped, the tip of the pin would appear to be bent. This would provide indication that the pin requires straightening even though the pin is perpendicular with the portion of the backplane surrounding the aperture into which the pin is mounted.
As noted above, as many as 10,000 pins are typically inserted into apertures of a single backplane. In a typical manufacturing operation, many pin-populated backplanes are assembled within relatively short periods of time. For example, in one manufacturing operation, 160 pin-populated backplanes can be assembled within a single day. Since each pin on the component side of each backplane must be straightened, and since there is such a large number of pins to be straightened, efficiency dictates that pluralities of pins be straightened simultaneously. However, when such mass pin straightening is considered, the above-mentioned problems resulting from the closeness of adjacent pins and warpage of the backplane pose serious difficulties.
Since the shanks of the pins are slender, it is important that the straightening forces not be excessive to the extent that the pins are damaged. Additionally, during the pin straightening operation, the portions of the pins which are mounted within apertures of the backplane must not move laterally. Otherwise, lateral movement of the pins within the apertures could result in damage to the backplane. Lateral pin movement within the apertures can occur when the backplane is permitted to move during the pin straightening operation. Thus, it is important that the backplane be rigidly secured to a fixture to prevent any of the straightening motion from being transmitted to the backplane. Further, it is important that the pins to be straightened be visible immediately before the assembly of the straightening facilities with the pins. If the pins are inserted into an enclosure, wherein the pins are not visible, and are then inserted into a straightening facility, there is no way to determine whether any of the pins were bent considerably beyond a position of assembly with the facility. In this instance, the bent pins could be deformed against the backplane by the straightening facility. If a straightening operation is then conducted, the backplane and other pins could be damaged.
An apparatus which holds the backplane flat in a rigid mounting with the pins visible and which applies relatively nonexcessive straightening forces to the pins is disclosed in a copending application filed on even date herewith in the name of W. M. Chisholm. The aforementioned application of W. M. Chisholm has been assigned Ser. No. 124662 by the U.S. Patent and Trademark Office. The disclosure of the above-mentioned application, Ser. No. 124662, filed on even date herewith is incorporated herein by reference thereto. The disclosure of copending application filed on even date herewith in the names of W. M. Chisholm and J. C. Dougherty and assigned Ser. No. 124683 by the U.S. Patent and Trademark Office, is also incorporated herein by reference thereto. Both of the aforementioned applications, Ser. Nos. 124662 and 124683, are assigned to the assignee of record in this application.
To insure that the pins are accurately straightened within acceptable tolerances, the pins should be examined after a straightening operation to determine whether further processing of the pins is required. Thus, it is important that the pins remain visible after the straightening operation to permit observation thereof. Further, there is a need for a process to measure and obtain data regarding the condition of the pins after a first straightening operation and to use the data to provide indication regarding the need for a second straightening operation and alterations to the straightening amplitude used in the first operation.